Abstract

A detailed phase diagram, revealing a variety of processes including various colloidalstructures of monodisperse charged colloidal particles from the colloidal chains, vortex rings, three-dimensional aggregation to a two-dimensional crystal under different frequencies, and strengths of an alternating electric field, is obtained for the first time. The occurrence of different colloidalstructures is driven by the electrohydrodynamic interaction and induced dipolar interaction near the polarized layer on the electrode. This simple colloidal system can be employed as a model system to understand the complex phase behavior of the assembly/aggregation of the nanoparticles and biomacromolecules under external perturbation. Detailed phase diagram provides vital guidance for the fabrication of desired colloidalstructures with single-particle resolution, which could be employed as a sort of templates for nanolithography or imprinting. Moreover, the sensitivity of the electrohydrodynamic interaction on the particle size and the dependence of the convective flow on the frequency and strength could be utilized in microfluidic devices for manipulating nanoparticles, biomacromolecules, and vesicles.

Received 10 November 2008Accepted 04 April 2009Published online 12 May 2009

Acknowledgments:

This work was supported by Academic Research Fund (ARF) Grant No. R-144-000-160-112. The authors thank Wei Tan's technical help in measuring the phase diagram and W.D. Ristenpart for helpful discussions. We also acknowledge C. Strom for a critical reading of the manuscript.

Article outline:I. INTRODUCTIONII. EXPERIMENTSA. Preparation of the colloidal suspensionB. Microscopic observationsC. Measurement of the particle velocitiesIII. RESULTS AND DISCUSSIONA. The detailed phase diagram of colloidalstructures under an AEFB. The theoretical modelsC. The formation mechanism of various colloidalstructuresD. The implication of the formation mechanisms of various colloidal phases controlled by the external electric fieldIV. CONCLUSION